Stepwise Construction of Heterobimetallic Cages by an Extended Molecular Library Approach

Abstract

Two novel heterobimetallic complexes, a trigonal-bipyramidal and a cubic one, have been synthesized and characterized using the same C-symmetric metalloligand, prepared by a simple subcomponent self-assembly strategy. Adopting the molecular library approach, we chose a mononuclear, preorganized iron(II) complex as the metalloligand capable of self-assembly into a trigonal-bipyramidal or a cubic aggregate upon coordination to cis-protected C-symmetric palladium(II) or unprotected tetravalent palladium(II) ions, respectively. The trigonal-bipyramidal complex was characterized by NMR and UV-vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray diffraction. The cubic structure was characterized by NMR and UV-vis spectroscopy and ESI-MS.

Dynamic Complex‐to‐Complex Transformations of Heterobimetallic Systems Influence the Cage Structure or Spin State of Iron(II) Ions

“…In conclusion, we presented the stepwise assembly of two heterobimetallic cages BP‐1 and CU‐1 from the same C 3 ‐symmetric metalloligand ML‐1 adopting the well‐implemented molecular library approach. Compared to previously reported diamagnetic complexes ML‐2 , BP‐2 , and CU‐2 the simple addition of a methyl group in 6‐position of the pyridyl ring leads to a substantial amount of steric strain and changes the spin state of the iron(II) cations from diamagnetic low spin to paramagnetic high spin. This impressively shows how rather small changes of the ligand system can cause tremendous changes of the complex properties.…”

“…Thus, it is possible to transfer all advantages of the subcomponent self‐assembly approach to systems consisting of more than one type of metal cation. However, to date only a few examples of heterobimetallic complexes have been reported that were built up from subcomponents …”

“…Paramagnetic complexes ML‐1 and BP‐1 showed a very high tendency to undergo subcomponent‐exchange reactions, resulting in the first reported complex‐to‐complex transformations of heterobimetallic complexes to heterobimetallic complexes in which metal‐bridging components are exchanged. In this case, 2‐formyl‐6‐methyl‐5‐(4′‐pyridyl)‐pyridine 1 could be replaced by sterically less crowded 2‐formyl‐5‐(4′‐pyridyl)pyridine 3 , transforming the high‐spin complexes into their low‐spin analogues . The cubic cage CU‐1 , however, was found to exchange 1 much less readily, probably because the opening angle of the sterically crowded metalloligand makes it kinetically and thermodynamically favourable to assemble the cubic structure.…”

A Tris(3‐pyridyl)stannane as a Building Block for Heterobimetallic Coordination Polymers and Supramolecular Cages

“…Ar adically different outcomeiso bserved in the coordination of 1 to CuPF 6 ,c ontaining aw eakly-coordinating anion. The 1:1 reaction of 1 with [Cu(NCMe) 4 ]PF 6 gives the complex [Cu(1)(NCMe)] 4 [PF 6 ] 4 in 91 %i solated yield ( Figure 4) (see Exper-imentalS ection). The X-ray crystal structure showsacage arrangementi nw hich four of the ligands 1 bridge the four Cu centres,u sing all three pyridyl arms, into ad iscrete [{Cu(1)(NC-Me)} 4 (&PF 6 )] 3 + cation.…”

“…[2] Severin and co-workersh ave overcome this tendency by incorporatinga dditional steric groups into bis(3-pyridyl) Fe clathrochelate ligandst op roduce Pd 6 L 12 12 + cages, [2] and have found that tuningt he sterics alters the size of the cage. [3] This metalloligand strategy for the construction of heterometallic supramolecular architectures has been successfully enacted for av ariety of mixed transition metals ystems, for example, Fe/Pd, [2,[4][5][6] Fe/Ru, [7] Fe/Co, [8,9] Co/ Mn [5] and Ru/Pd. [10,11] However,t he use of main group metalloligands to createmixed main group/transitionmetal heterometallic systems is rare.…”